This is an original planning guide. It is not a vendor manual, an official standard, or legal advice. Example addresses use documentation ranges. Review every command before you paste it.
What this hour is for
Correct time keeps logs, certificates, and authentication in order. The checker looks at a server you name. You do not open UDP 123 to the world, and you do not answer queries for the internet. A public reflector is the failure this page forbids.
Write the sources you trust, and write that clients you administer are the only clients. A documentation address is not a time source. If the offset is large, step the clock in a window, not during this reading.
One host. The cross-desk note about directory time is prose, not a second change.
The change you can finish
Apply nothing during the writing of the note. When the lab window opens, it is one change on the device named in the ticket. Read the draft, then the device, then decide.
Rollback is the file or the revision you saved first. You do not invent a rollback after the only copy is gone.
- Name the host you administer.
- Read the offset.
- Confirm it does not serve the world.
- Write the sources.
- Do not open UDP 123 to any.
- Do not step the clock in this hour.
Mistakes that outlive the command
NTP Explained and How to Check Time Sync goes wrong in a small set of ways. The list is here so the ticket can forbid them before the window.
- An NTP server open to the internet.
- A reflector left from a sample.
- Stepping a production clock during the reading.
- A documentation address used as the source.
- Two time systems changed at once.
Decisions to write down
One decision for NTP Explained and How to Check Time Sync: The host is yours. It does not serve the world. Sources are named. UDP 123 is not open to any. And the clock was not stepped.
Checks before you call it done
Confirm this before you call the change done: The hostname is written. The offset is written. The world cannot query it. Sources are written. And no port was opened. If one of those fails, stop.
Before you leave the device
NTP Explained and How to Check Time Sync ends when the hostname on the device matches the hostname in the ticket. If it does not, you are on the wrong box. Stop. A command that succeeded on the wrong box is not progress.
The draft stays a draft until a person has read the names in it. A generator does not log into the device and does not know which interface is the uplink. You delete a line that names a device, a zone, or a prefix you did not write down.
0.0.0.0/0 is not kept because a sample included it. A source you can say is the source you keep. 192.0.2.0/24, 198.51.100.0/24, 203.0.113.0/24, and 2001:db8::/32 are documentation. They belong in the note. They are not prefixes you type onto a production device because they appeared in a draft.
prompt-for-this is a reminder that a secret is missing. It is not a password, a key, a community string, or a pre-shared key you save in the ticket or in git. The real secret stays in the store.
One change is the window. A VLAN and a routing protocol and a VPN do not share it. If two things move and the result is wrong, you will not know which one did it. The next feature waits for its own page.
If the same step fails twice, stop for the day. The failure is the result. Adding a forum command beside a half-applied config produces a device nobody can rebuild. Restore the copy you took first.
A second person reads the device name and the change aloud. If they cannot find them in the ticket, the note is not done. Silence is not agreement. Then leave the device alone.
This page is a planning guide. It is not a vendor manual, not an official standard, and not a permission to touch a network you do not administer. The pillar guide owns the wider design. This page owns one lab proof.
Tools for this guide
These tools run in the browser on this site. They do not log into your machines.
Related pillar guides
More in this cluster
The pillar for this page, and the next published pages filed with it.
- Pillar: Network Troubleshooting Guide
- How-To: Testing WebSocket and gRPC Endpoints
- Explainer: Bufferbloat Explained
- Explainer: Cloud Region Latency Explained
Companion: System: Active Directory Fundamentals.